1. Field of the Invention
The present invention relates generally to an assist air supply system for assisting atomization of fuel injected through a fuel injection valve in an automotive internal combustion engine. More specifically, the invention relates to an assist air supply system which is designed for injecting pressurized air in the vicinity of fuel injected through the fuel injection valve in order to promote forming uniform fuel content air/fuel mixture and for providing better fuel combustion efficiency.
2. Description of the Background Art
In the recent years, there have been developed and proposed assist air supply systems for supplying an assist air in the vicinity of fuel injection valves for prompting atomization of injected fuel to aid in establishing uniform fuel distribution in an air/fuel mixture and in providing high combustion efficiency of fuel. In the conventionally proposed assist air supply system, the assist air is introduced from the air induction passage upstream of a throttle valve utilizing pressure difference between the upstream side and downstream side of the throttle valve.
Such prior proposed system encountered problems in providing uniformity of assist air pressure. Namely, as will be appreciated, the pressure difference between the upstream and the downstream of the throttle valve is reduced according to increases in the throttle valve open angle. This means that the assist air pressure at high engine speed and high engine load condition becomes insufficient for promoting atomization of fuel.